The present invention is concerned with improving the adhesion between a dielectric substrate and the heat sink or heat spreader attached to the substrate. More particularly, the present invention is concerned with electronic packages that have a heat sink or spreader as one of its components. In addition, the electronic packages include an electronic component such as a semiconductor chip. According to the present invention, the adhesive bond between the heat sink or spreader and dielectric substrate upon which the heat sink or spreader is located is greatly enhanced.
Integrated circuit chips are continually being fabricated with higher circuit densities and smaller geometries. The amount of power consumed employing these integrated circuit chips exhibiting increased circuit density also is increased, thereby increasing the amount of heat generated. This in turn places greater demands upon the efficiency of heat removal generated during package operation in order to assure that the operating parameters of these devices are maintained within specific tolerances to thereby prevent damage to the package from overheating.
One well known means for providing heat removal is to utilize a metal or ceramic heat sink or more typically referred to as a heat spreader as used hereinafter. The heat spreader, in many instances, has been connected to the integrated circuit components by employing an adhesive to directly bond to the organic or ceramic surfaces of the electronic components. One of the more common adhesive materials employed have been the epoxy based materials. However, the heat spreader material (e.g. copper, nickel-coated copper, aluminum, anodized aluminum, chromium on aluminum) does not adequately adhere to epoxy and difficulties exist in maintaining the bond during thermal cycling. In order to reduce delamination problems, it has been suggested to increase the thermal conduction of the epoxy by incorporating a thermoconductive metal or ceramic particle in the epoxy to thereby increase its CTE (coefficient of thermal expansion) to bring it more in line with that of the material of the heat spreader. Nevertheless, room for improvement still exists with respect to the bond between the heat spreader and epoxy material.
In addition, attempts to use silicon adhesives for such purposes have been carried out, but such adhesives exhibit bond strengths with the heat spreader that is only about ⅓ to about xc2xd the strength of the epoxy materials. Moreover, constituents of silicon adhesives have a tendency to migrate out thereby contaminating surfaces with a microthin coating which prevents subsequent attachment of other organic materials to the circuit boards such as photoresists, solder resists, and encapsulents. Furthermore, contamination is especially a problem for reworking components because heating the silicon during rework greatly increases the contamination and prevents any subsequent encapsulation or other non-silicon processes on the circuit board that may be required for rework.
In view of the foregoing discussion, it would be desirable to improve the adhesion between the heat spreader and adhesive that contacts the electronic components of the package in order to provide increased resistance to delamination and package cracking, while also assuring adequate thermal transport capability.
It would also be desirable to provide a process that achieves improved adhesion that is more efficient and easier to carry out than the processes now commonly practiced.
The present invention is concerned with an article that comprises a dielectric substrate and a heat spreader located adjacent the substrate. The heat spreader is typically metallic. In order to improve the adhesion between the dielectric substrate and the heat spreader, a layer of a codeposited ZnCr is provided intermediate the dielectric substrate and the heat spreader. In addition, the present invention is concerned with electronic packages that include an integrated circuit chip surrounded by a dielectric, a heat spreader located adjacent the dielectric substrate and a layer of codeposited ZnCr intermediate the dielectric substrate and the heat spreader.
The present invention is also concerned with the process for fabricating the above-defined article. In particular, the process of the present invention involves providing a layer of a codeposited ZnCr on at least one major surface of a heat spreader, and then laminating the heat spreader to a dielectric substrate. By adhering the heat spreader to the dielectric prior to such steps as positioning of the integrated circuit chip on the circuit board, delamination is prevented during subsequent processing steps because of the enhanced adhesion achieved by the present invention. Subsequent processing steps typically include baking, die attaching, post heating, ball grid array attaching and masking. Such processing steps subject the structure to relatively high temperatures which, without the tenacious bond formed according to the present invention, could result in separation or delamination of the heat spreader from the dielectric.
Still other objects and advantages of the present invention will become apparent by those skilled in the art from the following description, wherein it is shown and described only the preferred embodiments of the present invention, simply by illustration of the best mode contemplated of carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature and not as restrictive.